Pluto-bound craft seeks Manhattan-sized lump of ice

Desirable destinations at the fringes of the solar system can be hard to find. So NASA has enlisted its famous Hubble Space Telescope to search for a celestial body that its New Horizons spacecraft can visit once the craft has passed Pluto.

New Horizons is due to fly past the dwarf planet and its moons in July 2015. The hope is that it will then be able to check out one of many balls of ice left over from the solar system's birth – known as a Kuiper Belt Objects or KBOs, after the region in the outer solar system inhabited by Pluto. Hubble's job will be to spot a target KBO that lies on New Horizons' continued trajectory. A KBO has never been seen up close.

Ground telescopes have already turned up over 50 KBOs, but so far nothing that would be close enough for New Horizons to get a good look. A typical KBO might be no larger than Manhattan and as black as charcoal against the star-studded Sagittarius constellation. All in all that makes for a true needle-in-a-haystack hunt.

Using Hubble as well as ground-based resources will increase the chances of finding a suitable target from 40 to 90 per cent, says NASA. The space-based telescope can spot a KBO against the clutter of background stars by turning at the same rate as the objects are moving against background stars. That means the Hubble images show stars as streaks, and possible KBOs as pinpoint objects.

If Hubble succeeds at a pilot observation, designed to figure out if it has a chance of finding an appropriate KBO, NASA will devote more of its precious observing time to look for a second destination for New Horizons.

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